Untuple using `def` not `val`.

As retronym noted on #897, `val` forces to early.

2 files changed, 6 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index c1083d26d..991940f10 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -591,18 +591,19 @@ object desugar {
   /** Map n-ary function `(p1, ..., pn) => body` where n != 1 to unary function as follows:
    *
    *    x$1 => {
-   *      val p1 = x$1._1
+   *      def p1 = x$1._1
    *      ...
-   *      val pn = x$1._n
+   *      def pn = x$1._n
    *      body
    *    }
    */
-  def makeUnaryCaseLambda(params: List[ValDef], body: Tree)(implicit ctx: Context): Tree = {
+  def makeTupledFunction(params: List[ValDef], body: Tree)(implicit ctx: Context): Tree = {
     val param = makeSyntheticParameter()
     def selector(n: Int) = Select(refOfDef(param), nme.selectorName(n))
     val vdefs =
       params.zipWithIndex.map{
-        case(param, idx) => cpy.ValDef(param)(rhs = selector(idx))
+        case (param, idx) =>
+          DefDef(param.name, Nil, Nil, TypeTree(), selector(idx)).withPos(param.pos)
       }
     Function(param :: Nil, Block(vdefs, body))
   }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index f1e1d9286..4d2ab3552 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -624,7 +624,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
 
       val desugared =
         if (protoFormals.length == 1 && params.length != 1 && ptIsCorrectProduct(protoFormals.head)) {
-          desugar.makeUnaryCaseLambda(params, fnBody)
+          desugar.makeTupledFunction(params, fnBody)
         }
         else {
           val inferredParams: List[untpd.ValDef] =